The present invention relates to a method and a device for detecting a lane change and a curve, respectively.
A multitude of brake-control systems, e.g. anti-lock braking systems (ABS), traction control systems (TCS) and/or electronic stability programs (ESP) are known from the related art. Thus, for example, it is known from the German Patent No. 22 43 260 (corresponding to U.S. Pat. No. 3,909,070) to jointly adjust the braking action at the wheel brakes of the wheels of one axle along the lines of preventing wheel lock. Since the wheels of one axle can be rolling on road-surface sections having very different road/tire friction coefficients, it is necessary to preselect which of the wheels to be jointly controlled predefines the joint braking action. In this connection, it is known to provide two operating modes for a joint adjustment of the braking action at both wheels of an axle. In the one operating mode, the so-called select-low-mode, the joint adjustment of the braking action, generally of the braking pressure, is effected as a function of the wheel having the lower wheel speed. In the so-called select-high-mode, the joint adjustment of the braking action, generally of the braking pressure, is effected as a function of the wheel having the greater wheel speed.
Furthermore, methods for detecting curves or for calculating lateral acceleration are known in the brake-control systems. This is done, for example, by determining a speed difference between a left and a right vehicle wheel of one or two axles on multi-track vehicles (passenger cars/trucks). For this, reference is made by way of example to the German Published Patent Application No. 41 40 239.
When cornering with high lateral acceleration, at the beginning of ABS control, thus at the beginning of the braking-pressure control for avoiding wheel lock, the control response is adapted to this cornering. During a lane change by the vehicle, however, the lateral-acceleration value calculated from the wheel-speed sensors passes through the zero crossing and changes its operational sign. If an ABS braking is started in this changeover region in which the lateral acceleration crosses zero, then the controller detects only a small lateral-acceleration value and is unable to initiate special measures for the wheel-pressure modulation during the cornering, i.e. the lane-change maneuver. Because of this, the vehicle may be under-braked during extreme lane-change maneuvers and tend toward oversteering.
An object of the present invention is to design a lane-change detection (LCC, Lane Change Control) which is used for detecting a lane change outside of and within an ABS control (pressure modulation at the wheels) with the aid of wheel-speed sensors.
According to the present invention, a lane change by a motor vehicle is detected in a first variant of the present invention, such that
a lateral-acceleration variable representing the lateral acceleration of the vehicle and/or a yaw variable representing the yaw velocity is ascertained,
the change as a function of time of the lateral-acceleration variable and/or of the yaw variable is formed, and
a lane change is detected when the change as a function of time exceeds a specifiable threshold value.
This variant is particularly suitable for detecting a lane change when no wheel-lock control processes are present.
A second variant, preferably used when wheel-lock control processes are present, is directed toward a motor vehicle having at least two wheels arranged front and rear in the direction of travel. In this case, provision is made that
speed variables are acquired which represent the rotations of at least two wheels,
a velocity variable is ascertained representing the longitudinal velocity of the vehicle,
the difference is determined between the speed variable of the fastest rear wheel and the velocity variable,
a curve and/or a lane change is detected when a specifiable, large difference exists for a time duration of specifiable length.
Due to the reliable detection of a lane change according to the present invention, a change in the wheel-pressure modulation adapted to the lane-change situation can be carried out in the ABS controller. This leads to an increase in vehicle stability and an improvement in the instantaneous braking power during such maneuvers.
In an advantageous refinement of the first variant, speed variables are determined which represent the rotations of at least two wheels, and the lateral-acceleration variable and/or the yaw variable is ascertained as a function of the speed variables.
In an advantageous refinement of the second variant, the time duration is specified as a function of the difference, it being provided in particular that the time duration is selected to be longer in the case of a smaller difference than in the case of a larger difference.
It is also advantageous that, in reaction to a detected lane change,
the braking pressure is built up more quickly at the outside wheel brake than at the inside wheel brake, and/or
the braking pressure at the outside wheel brake is increased, and/or
a yaw moment buildup delay, which the vehicle features within an anti-lock control device, is prevented.
In addition, according to the second variant, the braking pressure at the wheels of the rear axle is adjusted according to the select-low-control principle, according to which the braking action at both rear wheels is regulated as defined by the unstable rear wheel.